U.S. patent application number 10/510839 was filed with the patent office on 2005-07-21 for optical disk medium and hub.
Invention is credited to Mizuno, Osamu, Nakamura, Tohru, Nishikiori, Keiji.
Application Number | 20050160443 10/510839 |
Document ID | / |
Family ID | 31492272 |
Filed Date | 2005-07-21 |
United States Patent
Application |
20050160443 |
Kind Code |
A1 |
Mizuno, Osamu ; et
al. |
July 21, 2005 |
Optical disk medium and hub
Abstract
An optical disk medium (20), comprising an optical disk medium
body (1) having a first layer (2), a second layer (2b) thinner than
the first layer (2), a recording layer (2a) between the first layer
(2) and the second layer (2b) and a center hold (3) at the center
thereof and a hub (10) formed of a magnetic substance material,
wherein the hub (10) is fixed to the optical disk medium body (1)
so as to close the center hole (3) in the movable state relative to
the optical disk medium body (1) within a specified range, the
surface of the optical disk medium body (1) on the second layer
(2b) side forms a light input surface, and a projection is not
substantially formed on the surface of the optical disk medium body
(1) on the light input surface side including the peripheral edge
of the center hole (3), whereby since the second layer (2b) can be
thinly and accurately formed, the optical disk medium suitable for
high-density recording can be provided at a low cost.
Inventors: |
Mizuno, Osamu; (Osaka-shi,
Osaka, JP) ; Nakamura, Tohru; (Katano-shi , Osaka,
JP) ; Nishikiori, Keiji; (Yawata-shi , Kyoto,
JP) |
Correspondence
Address: |
Merchant & Gould
P O Box 2903
Minneapolis
MN
55402-0903
US
|
Family ID: |
31492272 |
Appl. No.: |
10/510839 |
Filed: |
October 8, 2004 |
PCT Filed: |
July 7, 2003 |
PCT NO: |
PCT/JP03/08632 |
Current U.S.
Class: |
720/721 ;
G9B/11.048; G9B/23.005; G9B/7.159; G9B/7.16 |
Current CPC
Class: |
G11B 11/10584 20130101;
G11B 7/24047 20130101; G11B 23/0035 20130101; G11B 7/24097
20130101 |
Class at
Publication: |
720/721 |
International
Class: |
G11B 023/03; G11B
007/24 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 6, 2002 |
JP |
2002-228859 |
Claims
1. An optical disk medium, comprising: an optical disk medium body
including a first layer, a second layer thinner than the first
layer, and a recording layer between the first layer and the second
layer and including a center hole at a center thereof, and a hub
made of a magnetic material, wherein the hub is confined with the
optical disk medium body in such a manner that the hub is movable
with respect to the optical disk medium body within a predetermined
range and that the hub covers the center hole, a surface of the
optical disk medium body on a side of the second layer is a
light-incident surface, and there is substantially no protrusion
formed on the surface of the optical disk medium body on the
light-incident surface side that includes an edge along the center
hole.
2. The optical disk medium according to claim 1, wherein a surface
for fitting to a turntable of a driving device is the
light-incident surface.
3. The optical disk medium according to claim 1, wherein a
confinement portion for confining the hub is provided in the first
layer.
4. The optical disk medium according to claim 3, wherein the
confinement portion is provided outside a range of a thickness of
the first layer.
5. The optical disk medium according to claim 3, wherein the
confinement portion is provided within a range of a thickness of
the first layer.
6. The optical disk medium according to claim 1, wherein the hub
includes an attracted plane on which a magnetic attractive force
acts and a flange formed substantially in parallel with the
attracted plane and along an edge of the attracted plane, at the
flange, the hub is confined with the optical disk medium body, and
a substantially ring-shaped contacting region at which the flange
and the optical disk medium body contact has an inner diameter of
11.8 mm or more and an outer diameter of 13.3 mm or less.
7. The optical disk medium according to claim 1, wherein the hub
includes an attracted plane on which a magnetic attractive force
acts and a flange formed substantially in parallel with the
attracted plane and along an edge of the attracted plane, at the
flange, the hub is confined with the optical disk medium body, and
a region of the optical disk medium body that contacts with the
flange has a thickness of 0.5 mm or more.
8. A hub that is attached to an optical disk medium body so as to
cover a center hole formed at a center of the optical disk medium
body and for mounting the optical disk medium body on a turntable
by utilizing a magnetic attractive force, the hub being made of a
magnetic material and comprising: an attracted plane on which the
magnetic attractive force acts; and a plurality of first latching
strips and a plurality of second latching strips, the first
latching strips and the second latching strips being located at
positions different from each other in a direction of the normal of
the attracted plane.
9. The hub according to claim 8, wherein the hub is attached to the
optical disk medium body in such a manner that at least a part of
the optical disk medium body at an edge along the center hole is
positioned between the plurality of first latching strips and the
plurality of second latching strips.
10. The hub according to claim 8, wherein the hub is attached to
the optical disk medium body in such a manner that the hub is
movable with respect to the optical disk medium body within a
predetermined range.
11. The hub according to claim 8, wherein the plurality of first
latching strips are formed rigidly with the attracted plane, and
the plurality of second latching strips can be displaced
elastically with respect to the attracted plane.
12. The hub according to claim 8, wherein when the hub is attached
to the optical disk medium body, the plurality of second latching
strips make contact with an edge along the center hole so as to be
displaced elastically with respect to the attracted plane and
thereafter are restored elastically, thereby the hub is attached to
the optical disk medium body in such a manner that at least a part
of the edge along the center hole is positioned between the
plurality of first latching strips and the plurality of second
latching strips.
13. The hub according to claim 8, further comprising a plurality of
leg portions that extend in a direction substantially perpendicular
to the attracted plane, wherein the plurality of second latching
strips respectively are provided at tip ends of the plurality of
leg portions and protrude outwardly substantially in parallel with
the attracted plane, and the plurality of first latching strips
protrude outwardly substantially in parallel with the attracted
plane.
14. The hub according to claim 13, wherein a diameter of a circle
that is inscribed in the plurality of leg portions is larger than a
diameter of a circle that is inscribed in the center hole.
15. The hub according to claim 8, further comprising a plurality of
walls that extend substantially perpendicular to the attracted
plane, wherein the plurality of first latching strips respectively
are provided at tip ends of the plurality of walls and protrude
outwardly substantially in parallel with the attracted plane, and
the hub has a substantially hat shaped disk form as a whole.
16. The hub according to claim 8, wherein the plurality of first
latching strips and the attracted plane are substantially coplanar
with each other.
17. An optical disk medium, comprising: an optical disk medium body
including a first layer, a second layer thinner than the first
layer, and a recording layer between the first layer and the second
layer and including a center hole at a center thereof and a hub
attached so as to cover the center hole, wherein a surface of the
optical disk medium body on a side of the second layer is a
light-incident surface, and the hub is the hub according to claim
8.
18. The optical disk medium according to claim 17, wherein in a
state where the optical disk medium is mounted on a turntable of a
driving device, the second latching strips, which are the nearest
to the turntable, do not protrude from the surface of the optical
disk medium body on a side of the light-incident surface, and the
surface of the optical disk medium body on the side of the
light-incident surface contacts with a surface of the
turntable.
19. The optical disk medium according to claim 17, wherein the hub
is confined with the optical disk medium body in such a manner that
the hub is movable with respect to the optical disk medium body
within a predetermined range.
20. The optical disk medium according to claim 17, wherein the hub
further includes a plurality of leg portions that extend in a
direction substantially perpendicular to the attracted plane, the
plurality of second latching strips respectively are provided at
tip ends of the plurality of leg portions and protrude outwardly
substantially in parallel with the attracted plane., a plurality of
cut-away portions are formed at a part of an edge along the center
hole, the cut-away portions extending outwardly, and a diameter of
a circle that is inscribed in edges of the plurality of cut-away
portions is larger than a diameter of a circle that is
circumscribed around the plurality of leg portions.
21. The optical disk medium according to claim 20, wherein a
concave portion in which each of the plurality of second latching
strips is to be fitted is formed at an edge of each of the
plurality of cut-away portions on the light-incident surface side,
and assuming that a depth of the concave portion in a direction of
the normal of the light-incident surface is H and a thickness of
the plurality of second latching strips in the direction of the
normal is h, a relationship of H>h is satisfied.
22. The optical disk medium according to claim 17, wherein there is
substantially no protrusion formed on the surface on the
light-incident surface side that includes an edge along the center
hole.
23. The optical disk medium according to claim 17, wherein a
diameter of a circle that is inscribed in a plurality of regions
where the plurality of first latching strips and the optical disk
medium body contact is 11.8 mm or more, and a diameter of a circle
that is circumscribed around the plurality of regions is 13.3 mm or
less.
24. The optical disk medium according to claim 17, wherein a
thickness of the optical disk medium body at a region where the
optical disk medium body contacts with the first latching strips is
0.5 mm or more.
Description
TECHNICAL FIELD
[0001] The present invention relates to an optical disk medium in
which light, in particular a laser beam, contributes to a
recording/reproducing procedure and relates to a hub, made of a
magnetic material, that is for mounting an optical disk medium on
an optical disk drive by utilizing a magnetic attractive force.
BACKGROUND ART
[0002] Examples of conventional optical disk media with hubs
attached thereto include a minidisc (hereinafter abbreviated as MD)
and an optical disk medium with a hub that is used in a 3.5-inch or
a 5-inch group magneto-optical data file device, for example.
[0003] JP 3072658 B shows one example of the optical disk medium
and the hub for MD.
[0004] The magneto-optical recording with respect to MDs or the
like is a kind of vertical thermo-magnetic recording. That is, with
respect to a medium whose coercive force has been reduced partially
by application of heat with a laser beam, the recording is
conducted by applying a vertical magnetic field modulated with a
recording signal so as to magnetize the medium and form vertical
magnetic domains. This modulated vertical magnetic field is
generated by a magnetic head. The reproduction is conducted by
detecting the rotation of a reflecting-polarized plane due to the
Kerr effect so as to read a magnetizing direction of the vertical
magnetic domains.
[0005] Although MDs mainly are targeted for recording music data,
optical disk media generally are required to have capabilities of
further recording and storing massive amounts of data, including
data and images. To this end, the optical disk media are required
to have a larger capacity, which means that higher-density optical
disk media are demanded strongly.
[0006] The following are explanations of a conventional optical
disk medium and hub, taking those described in the above-mentioned
JP 3072658 B as an example. FIG. 11 is an exploded perspective view
showing their overall configuration. FIG. 12A is a cross-sectional
view showing one step for attaching the hub to an optical disk
medium body. FIG. 12B is a cross-sectional view of the conventional
optical disk medium with the hub attached thereto. FIG. 12C is a
cross-sectional view showing a state where the conventional optical
disk medium is mounted on a turntable of a driving device. For
convenience of explanations, the longitudinal direction of the
sheet will be referred to as a "height direction".
[0007] In FIG. 11, FIG. 12A and FIG. 12B, reference numeral 101
denotes an optical disk medium body, and a MD is exemplified herein
for the explanation. The optical disk medium body 101 mainly is
made up of a substrate 102 in a substantially disk form, and on one
surface of the substrate 102 a recording layer 102a is provided.
Reference numeral 102c denotes a protective layer provided on a
surface of the recording layer 102a in order to protect the
recording layer 102a from oxidization and the like. In the
recording layer 102a, a signal portion region is formed in which
information is recorded. A laser beam that allows information to be
recorded, reproduced and erased is applied to the recording layer
102a from a side of the substrate 102 by way of the substrate 102.
That is, a light-incident surface is a lower surface of the
substrate 102 in FIG. 12B.
[0008] Therefore, the substrate 102 functions as a cover layer of
the recording layer 102a when being irradiated with a laser
beam.
[0009] As shown in FIG. 12A and FIG. 12B, a center hole 103 for
centering is provided at the center of the substrate 102. On a
surface of the substrate 102 on the side where the recording layer
102a is provided, a concave portion 106 is formed at an edge along
the center hole 103 so as to be recessed from the region where the
recording layer 102a is provided. Furthermore, on a surface
(light-incident surface) of the substrate 102 that is opposite to
the side where the recording layer 102a is provided, a convex
portion 104 is formed at an edge along the center hole 103 so as to
protrude from a region outside the convex portion.
[0010] Reference numeral 110 denotes the hub, made of a magnetic
material, having a disk form like a substantially hat shape and a
hub hole 111 is bored at the center of the hub to allow the
handling with a jig or the like. Reference numeral 112 denotes an
attracted plane in a planar disk form that occupies most of the hub
110, and 113 denotes a flange that is displaced from the attracted
plane 112 in the height direction. A wall 114 connects between the
attracted plane 112 and the flange 113.
[0011] From the state shown in FIG. 12A, the flange 113 of the hub
110 is inserted into the concave portion 106 of the substrate 102,
so as to bring a lower surface of the flange 113 into contact with
a bottom surface 106a of the concave portion 106. Thereafter, heat
and pressure are applied to the edge of the concave portion 106 so
as to thermally deform the same, whereby, as shown in FIG. 12B, a
protrusion 107 is formed to cover an upper surface of the flange
113. As a result, the flange 113 is fixed in the concave portion
106, whereby an optical disk medium 100 can be obtained.
[0012] Referring to FIG. 12C, a procedure for mounting the optical
disk medium 100 with the hub 110 of FIG. 12B on the turntable will
be explained below, where the turntable is attached to a rotary
shaft of a spindle motor of the driving device (not illustrated).
In FIG. 12C, reference numeral 120 denotes the turntable, at the
center of which a convex portion 123 protrudes to include a
permanent magnet 121 embedded therein. During the insertion of the
convex portion 123 of the turntable 120 into the center hole 103 of
the substrate 102, a tapered portion 124 at the top of the convex
portion 123 enables the correction of the displacement of the
center of the optical disk medium body 101 from the rotation center
of the turntable 120. Then, a magnetic attractive force by the
permanent magnet 121 acts on the attracted plane 112 of the hub 110
so that the edge of the substrate 102 along the center hole 103 is
positioned between the flange 113 of the hub 110 and the turntable
120, whereby the optical disk medium body 101 is held on the
turntable 120. In this step, a lower surface 104a of the convex
portion 104 of the substrate 102 makes contact with an upper
surface of a flange 122 that is formed at the edge of the turntable
120. Thereby, the optical disk medium body 101 is positioned in the
direction of the rotary shaft (the height direction). Furthermore,
an inner wall surface of the center hole 103 of the substrate 102
makes contact with a cylindrical outer wall surface of the convex
portion 123 protruding from the center of the turntable 120,
whereby the optical disk medium body 101 is aligned in the radius
direction.
[0013] In this state, a collected light beam is applied from the
side of the substrate 102. The laser beam passes through the
substrate 102 and is converged on the recording layer 102a. The
reproduction of information is enabled by detecting reflected light
that has been modulated in accordance with the information recorded
on the recording layer 102a and demodulating the same. In the
magneto-optical recording technique adopted for MDs or the like,
the recording and the erasing of information are enabled by
irradiating the recording layer 102a with an intense laser beam
from one side of the optical disk medium 101 so as to heat the
recording layer 102a while applying a modulated magnetic field from
the other side.
[0014] The above-described conventional optical disk medium 100,
however, has the following problems.
[0015] That is, the convex portion 104 protruding toward the
light-incident surface side becomes a hindrance to a higher density
optical disk medium. This will be described below in detail.
[0016] As previously described, optical disk media are required to
have a large capacity so as to allow for the recording of image
data and the like, which results in a demand for higher-density
optical disk media. One of the effective means for realizing a
higher density is to make an optical spot formed in the recording
layer minute so as to enhance a spatial resolution. A size of this
optical spot is proportional to .lambda./(2.times.NA), where
.lambda. represents a wavelength of a laser beam and NA represents
a numerical aperture of an objective lens. Therefore, in order to
obtain a higher density, it is effective to decrease .lambda. and
increase NA.
[0017] In the normal heat mode recording that does not utilize
super-resolution, a width of a recording track and a bit length in
a linear direction both can be made minute proportional to
.lambda./(2.times.NA), whereby the recording density can be
increased proportional to the square of the inverse of
.lambda./(2.times.NA).
[0018] When .lambda. decreases and NA increases, however, the
tolerance of a region through which a laser beam passes, i.e., the
cover layer (substrate 102), to the occurrence of various
aberrations decreases rapidly. For instance, when NA is increased,
the tolerance of a tilt of the cover layer with reference to the
laser optical axis decreases proportionally to the cube of the
inverse of the NA. In addition, the tolerance of the tilt of the
cover layer with reference to the laser optical axis is
proportional to .lambda..
[0019] For instance, when a system with NA=0.6 and .lambda.=700 nm
is substituted for a system with NA=0.9 and .lambda.=400 nm,
although the recording density is increased by about seven times,
the tolerance of the tilt of the cover layer should be controlled
to about 1/6 of that prior to the change.
[0020] In addition to that, when NA is increased, the tolerance of
a thickness of the cover layer (substrate 102) decreases
proportionally to the fourth power of the inverse of the NA.
[0021] On the other hand, the tolerance to the tilt increases
proportionally to the inverse of the thickness of the cover layer.
In other words, the tolerance to the tilt increases with decreasing
the thickness of the cover layer. For instance, in the above-stated
numerical example, in order to make the tolerance to the tilt after
the change of the conditions for .lambda. and NA substantially
equal to that prior to the change, the thickness of the cover layer
should be 1/6 of that prior to the change. However, a range of the
tolerance to the cover layer thickness is not enlarged.
[0022] From these points, in order to realize a higher density
optical disk medium, an optical disk medium with a thin cover layer
has been proposed, and technology for making the cover layer thin
and uniform in thickness receives attention.
[0023] The thickness of the cover layer according to this
technology is considerably thin, about 100 .mu.m, and its error in
thickness should be controlled to about several .mu.m. In the
above-described conventional example shown in FIG. 11 and FIGS. 12A
to 12C, however, the convex portion 104 is present on the
light-incident surface side of the cover layer (substrate 102),
which becomes a significant hindrance to the formation of a cover
layer that is thin and uniform in thickness, so that sufficient
optical properties cannot obtained. This brings about the problem
in that a higher density optical disk medium cannot be
realized.
DISCLOSURE OF THE INVENTION
[0024] In order to cope with the above-stated problems, it is an
object of the present invention to provide an optical disk medium
and a hub that enable a higher density optical disk medium.
[0025] An optical disk medium of the present invention includes: an
optical disk medium body including a first layer, a second layer
thinner than the first layer, and a recording layer between the
first layer and the second layer and including a center hole at a
center thereof, and a hub made of a magnetic material. The hub is
confined with the optical disk medium body in such a manner that
the hub is movable with respect to the optical disk medium body
within a predetermined range and that the hub covers the center
hole. A surface of the optical disk medium body on a side of the
second layer is a light-incident surface, and there is
substantially no protrusion formed on the surface of the optical
disk medium body on the light-incident surface side that includes
an edge along the center hole.
[0026] A hub of the present invention is attached to an optical
disk medium body so as to cover a center hole formed at a center of
the optical disk medium body and is for mounting the optical disk
medium body on a turntable by utilizing a magnetic attractive
force. The hub is made of a magnetic material and includes: an
attracted plane on which the magnetic attractive force acts; and a
plurality of first latching strips and a plurality of second
latching strips, the first latching strips and the second latching
strips being located at positions different from each other in a
direction of the normal of the attracted plane.
BRIEF DESCRIPTION OF DRAWINGS
[0027] FIG. 1A is a cross-sectional view of an optical disk medium
body and a hub of Embodiment 1 of the present invention, which
shows a state before the attachment of the hub, FIG. 1B is a
cross-sectional view of an optical disk medium according to
Embodiment 1 of the present invention, which shows a state where
the hub has been attached, FIG. 1C is a cross-sectional view
showing a state immediately before the optical disk medium
according to Embodiment 1 of the present invention is mounted on a
turntable of a driving device, and FIG. 1D is a cross-sectional
view showing a state where the optical disk medium according to
Embodiment 1 of the present invention has been mounted to the
turntable of the driving device.
[0028] FIG. 2A is a cross-sectional view of an optical disk medium
body and a hub of Embodiment 2 of the present invention, which
shows a state before the attachment of the hub, and FIG. 2B is a
cross-sectional view of an optical disk medium according to
Embodiment 2 of the present invention, which shows a state where
the hub has been attached.
[0029] FIG. 3A is a plan view of an optical disk medium body of
Embodiment 3 of the present invention, and FIG. 3B is a
cross-sectional view taken along an arrow 3B-3B of FIG. 3A.
[0030] FIG. 4A is a plan view of a hub of Embodiment 3 of the
present invention, FIG. 4B is a cross-sectional view taken along an
arrow 4B-4B of FIG. 4A and FIG. 4C is a cross-sectional view taken
along an arrow 4C-4C of FIG. 4A.
[0031] FIG. 5A is a cross-sectional view of an optical disk medium
body and a hub of Embodiment 3 of the present invention, which
shows a state before the attachment of the hub, and FIG. 5B is a
cross-sectional view of an optical disk medium according to
Embodiment 3 of the present invention, which shows a state where
the hub has been attached.
[0032] FIG. 6A is a plan view of a hub of Embodiment 4 of the
present invention, and FIG. 6B is a cross-sectional view taken
along an arrow 6B-6B of FIG. 6A.
[0033] FIG. 7A is a cross-sectional view of an optical disk medium
body and a hub of Embodiment 4 of the present invention, which
shows a state before the attachment of the hub, and FIG. 7B is a
cross-sectional view of an optical disk medium according to
Embodiment 4 of the present invention, which shows a state where
the hub has been attached.
[0034] FIG. 8 is a plan view of an optical disk medium body of
Embodiment 5 of the present invention.
[0035] FIG. 9 is a plan view of a hub of Embodiment 5 of the
present invention.
[0036] FIG. 10 is an expanded cross-sectional view of a portion in
the vicinity of a center hole of an optical disk medium of
Embodiment 6 of the present invention.
[0037] FIG. 11 is an exploded perspective view showing the
conventional optical disk medium and the hub.
[0038] FIG. 12A is a cross-sectional view of the conventional
optical disk medium body and hub, which shows a state before the
attachment of the hub, FIG. 12B is a cross-sectional view of the
conventional optical disk medium, which shows a state where the hub
has been attached, and FIG. 12C is a cross-sectional view showing a
state where the conventional optical disk medium has been mounted
on the turntable of the driving device.
BEST MODE FOR CARRYING OUT THE INVENTION
[0039] The optical disk medium of the present invention includes:
an optical disk medium body including a first layer, a second layer
thinner than the first layer, and a recording layer between the
first layer and the second layer and including a center hole at a
center thereof; and a hub made of a magnetic material. The hub is
confined with the optical disk medium body in such a manner that
the hub is movable with respect to the optical disk medium body
within a predetermined range and that the hub covers the center
hole. A surface of the optical disk medium body on a side of the
second layer is a light-incident surface, and there is
substantially no protrusion formed on the surface of the optical
disk medium body on the light-incident surface side that includes
an edge along the center hole.
[0040] According to such an optical disk medium of the present
invention, the second layer can be formed thinner and precisely,
and therefore an optical disk medium suitable for high-density
recording can be provided at a low cost.
[0041] In the above optical disk medium of the present invention,
it is preferable that a surface for fitting to a turntable of a
driving device is the light-incident surface. With this
configuration, the distance between the recording layer and an
optical head that emits a laser beam can be stabilized, so that the
signal quality can be enhanced. As a result, an optical disk medium
suitable for high-density recording can be provided.
[0042] In the above optical disk medium of the present invention,
it is preferable that a confinement portion for confining the hub
is provided in the first layer. The confinement portion is provided
in the first layer located on the opposite side of the
light-incident surface, which facilitates the formation of a thin
second layer with a uniform thickness on the light-incident surface
side and the enhancement of the flatness of the surface on the
light-incident surface side. As a result, an optical disk medium
suitable for high-density recording can be provided.
[0043] In the above, the confinement portion may be provided
outside a range of a thickness of the first layer. This allows the
hub to be attached easily even to a thin substrate.
[0044] Alternatively, the confinement portion may be provided
within a range of a thickness of the first layer. This allows a
part or all of the thickness of the hub to be included in the
thickness of the substrate, whereby a low-profile optical disk
medium with fewer protrusions can be provided. Furthermore, the
confinement portion can be formed relatively easily, and the
flatness of the optical disk medium body can be enhanced.
[0045] In the above optical disk medium of the present invention,
preferably, the hub includes an attracted plane on which a magnetic
attractive force acts and a flange formed substantially parallel to
the attracted plane and along an edge of the attracted plane. At
the flange, the hub is confined with the optical disk medium body,
and a substantially ring-shaped contacting region at which the
flange and the optical disk medium body contact has an inner
diameter of 11.8 mm or more and an outer diameter of 13.3 mm or
less. With this configuration, when the optical disk medium is
mounted on a turntable of a driving device, the warp of the optical
disk medium body can be reduced.
[0046] In the above optical disk medium of the present invention,
preferably, the hub includes an attracted plane on which a magnetic
attractive force acts and a flange formed substantially parallel to
the attracted plane and along an edge of the attracted plane. At
the flange, the hub is confined with the optical disk medium body,
and a region of the optical disk medium body that contacts with the
flange has a thickness of 0.5 mm or more. With this configuration,
when the optical disk medium is mounted on a turntable of a driving
device, the warp of the optical disk medium body can be
reduced.
[0047] Meanwhile, the hub of the present invention is attached to
an optical disk medium body so as to cover a center hole formed at
a center of the optical disk medium body and is for mounting the
optical disk medium body on a turntable by utilizing a magnetic
attractive force. The hub is made of a magnetic material and
includes: an attracted plane on which the magnetic attractive force
acts; and a plurality of first latching strips and a plurality of
second latching strips, the first latching strips and the second
latching strips being located at positions different from each
other in a direction of the normal of the attracted plane.
[0048] According to such a hub of the present invention, the hub
can be connected with the optical disk medium body easily without
the necessity of specific melting and deforming procedures.
Therefore, there is no need to provide a protrusion for attaching a
hub on a surface of the optical disk medium body on the
light-incident surface side including an edge along the center
hole. As a result, an optical disk medium suitable for high-density
recording can be provided at a low cost.
[0049] Preferably, the above hub of the present invention is
attached to the optical disk medium body in such a manner that at
least a part of the optical disk medium body at an edge along the
center hole is positioned between the plurality of first latching
strips and the plurality of second latching strips. This can
simplify the attachment structure of the hub to the optical disk
medium body.
[0050] The above hub of the present invention preferably is
attached to the optical disk medium body in such a manner that the
hub is movable with respect to the optical disk medium body within
a predetermined range. This configuration can avoid the warp of the
optical disk medium body and the occurrence of internal stress,
which result from differences in dimensional change and deformation
between the hub and the optical disk medium body caused by a change
in temperature and humidity. Furthermore, when the optical disk
medium is mounted on the turntable of the driving device, the
centering of the optical disk medium body can be conducted easily
with respect to the turntable.
[0051] In the above hub of the present invention, preferably, the
plurality of first latching strips are formed rigidly with the
attracted plane, and the plurality of second latching strips can be
displaced elastically with respect to the attracted plane. Since
the first latching strips have high stiffness, when the optical
disk medium is mounted on the turntable of the driving device, the
hub can be positioned with respect to the turntable in the height
direction precisely. Thereby, a stable attractive force can be
attained. Furthermore, since the second latching strips can be
displaced elastically, the hub can be attached to the optical disk
medium body easily without the necessity of specific manufacturing
equipment, and therefore an optical disk medium can be realized at
a low cost.
[0052] Preferably, when the above hub of the present invention is
attached to the optical disk medium body, the plurality of second
latching strips make contact with an edge along the center hole so
as to be displaced elastically with respect to the attracted plane
and thereafter are restored elastically, thereby the hub is
attached to the optical disk medium body in such a manner that at
least a part of the edge along the center hole is positioned
between the plurality of first latching strips and the plurality of
second latching strips. With this configuration, the hub can be
attached to the optical disk medium body easily without the
necessity of specific manufacturing equipment, and therefore an
optical disk medium can be realized at a low cost.
[0053] Preferably, the above hub of the present invention further
includes a plurality of leg portions that extend in a direction
substantially perpendicular to the attracted plane. The plurality
of second latching strips respectively are provided at tip ends of
the plurality of leg portions and protrude outwardly substantially
parallel to the attracted plane, and the plurality of first
latching strips protrude outwardly substantially parallel to the
attracted plane. With this configuration, second latching strips
that can be displaced elastically can be formed easily.
[0054] Herein, it is preferable that a diameter of a circle that is
inscribed in the plurality of leg portions is larger than a
diameter of a circle that is inscribed in the center hole. With
this configuration, the leg portions do not adversely affect the
centering operation of the optical disk medium body with respect to
the turntable of the driving device. Therefore, when the optical
disk medium is mounted on the turntable of the driving device, a
stable centering operation can be realized.
[0055] Preferably, the above hub of the present invention further
includes a plurality of walls that extend substantially
perpendicular to the attracted plane. The plurality of first
latching strips respectively are provided at tip ends of the
plurality of walls and protrude outwardly in substantially parallel
with the attracted plane, and the hub has a substantially hat
shaped disk form as a whole. With this configuration, first
latching strips having high stiffness can be formed easily.
Furthermore, the strength of the hub can be enhanced.
[0056] In the above hub of the present invention, the plurality of
first latching strips and the attracted plane may be substantially
coplanar with each other. With this configuration, a relative
positional accuracy between the first latching strips and the
attracted plane can be enhanced in the direction of the normal of
the attracted plane. Therefore, when the optical disk medium is
mounted on the turntable of the driving device, the positional
accuracy of the attracted plane on which the magnetic attractive
force acts with respect to the turntable can be improved
significantly. Thus, a hub enabling the generation of a stable
attractive force can be provided.
[0057] A second optical disk medium of the present invention
includes: an optical disk medium body including a first layer, a
second layer thinner than the first layer, and a recording layer
between the first layer and the second layer and including a center
hole at a center thereof and a hub attached so as to cover the
center hole. A surface of the optical disk medium body on a side of
the second layer is a light-incident surface, and the hub is the
above hub of the present invention.
[0058] According to such a second optical disk medium of the
present invention, the hub can be connected with the optical disk
medium body easily without the necessity of specific melting and
deforming procedures. Therefore, there is no need to provide a
protrusion for attaching a hub on a surface of the optical disk
medium body on the light-incident surface side including an edge
along the center hole. As a result, an optical disk medium suitable
for high-density recording can be provided at a low cost.
[0059] Preferably, in a state where the above second optical disk
medium of the present invention is mounted on a turntable of a
driving device, the second latching strips, which are the nearest
to the turntable, do not protrude from the surface of the optical
disk medium body on a side of the light-incident surface, and the
surface of the optical disk medium body on the side of the
light-incident surface contacts with a surface of the turntable.
With this configuration, when the optical disk medium is mounted on
the turntable of the driving device, the second latching strips do
not affect the attitude of the optical disk medium body and the
surface on the light-incident side and the surface of the turntable
can establish surface contact therebetween, and therefore the
optical disk medium can be mounted on the turntable stably.
Furthermore, the distance between the recording layer and an
optical head that emits a laser beam can be stabilized, so that a
signal quality can be enhanced. As a result, an optical disk medium
suitable for high-density recording can be provided.
[0060] In the above second optical disk medium of the present
invention, it is preferable that the hub is confined with the
optical disk medium body in such a manner that the hub is movable
with respect to the optical disk medium body within a predetermined
range. This configuration can avoid the warp of the optical disk
medium body and the occurrence of internal stress, which result
from differences in dimensional change and deformation between the
hub and the optical disk medium body caused by a change in
temperature and humidity. Furthermore, when the optical disk medium
is mounted on the turntable of the driving device, the centering of
the optical disk medium body can be conducted easily with respect
to the turntable.
[0061] In the above second optical disk medium of the present
invention, preferably, the hub further includes a plurality of leg
portions that extend in a direction substantially perpendicular to
the attracted plane. The plurality of second latching strips
respectively are provided at tip ends of the plurality of leg
portions and protrude outwardly in substantially parallel with the
attracted plane. A plurality of cut-away portions are formed at a
part of an edge along the center hole, the cut-away portions
extending outwardly, and a diameter of a circle that is inscribed
in edges of the plurality of cut-away portions is larger than a
diameter of a circle that is circumscribed around the plurality of
leg portions. With this configuration, the hub can be kept in a
movable state with respect to the optical disk medium body in a
direction along a plane in parallel with the light-incident
surface.
[0062] In the above second optical disk medium of the present
invention, preferably, a concave portion in which each of the
plurality of second latching strips is to be fitted is formed at an
edge of each of the plurality of cut-away portions on the
light-incident surface side, and assuming that a depth of the
concave portion in a direction of the normal of the light-incident
surface is H and a thickness of the plurality of second latching
strips in the direction of the normal is h, a relationship of
H>h is satisfied. With this configuration, when the optical disk
medium is mounted on the turntable of the driving device, the
second latching strips retract in the concave portions and do not
protrude from the surface on the light-incident side. Therefore,
the surface on the light-incident side and the surface of the
turntable can establish surface contact therebetween, so that the
optical disk medium can be mounted on the turntable stably.
Furthermore, the distance between the recording layer and an
optical head that emits a laser beam can be stabilized, so that a
signal quality can be enhanced. As a result, an optical disk medium
suitable for high-density recording can be provided.
[0063] In the above second optical disk medium of the present
invention, preferably, there is substantially no protrusion formed
on the surface on the light-incident surface side that includes an
edge along the center hole. With this configuration, the second
layer can be formed thinner and precisely, and therefore an optical
disk medium suitable for high-density recording can be provided at
a low cost.
[0064] In the above second optical disk medium of the present
invention, preferably, a diameter of a circle that is inscribed in
a plurality of regions where the plurality of first latching strips
and the optical disk medium body contact is 11.8 mm or more, and a
diameter of a circle that is circumscribed around the plurality of
regions is 13.3 mm or less. With this configuration, when the
optical disk medium is mounted on a turntable of a driving device,
the warp of the optical disk medium body can be reduced.
[0065] In the above second optical disk medium of the present
invention, preferably, a thickness of the optical disk medium body
at a region where the optical disk medium body contacts with the
first latching strips is 0.5 mm or more. With this configuration,
when the optical disk medium is mounted on a turntable of a driving
device, the warp of the optical disk medium body can be
reduced.
[0066] The following describes specific embodiments of the present
invention in detail, with reference to FIG. 1 to FIG. 10. In the
drawings, a cross-section of a disk is shown by way of a cut end
face only for the sake of intelligibility. Note here that the
present invention is not limited to the following embodiments.
[0067] In the following descriptions, a direction normal to a
light-incident surface of the optical disk medium (direction of a
rotation center axis) will be referred to as a "height
direction".
[0068] (Embodiment 1)
[0069] FIG. 1A is an exploded cross-sectional view of an optical
disk medium body and a hub that constitute an optical disk medium
of Embodiment 1 of the present invention, and FIG. 1B is a
cross-sectional view of the optical disk medium of Embodiment 1 of
the present invention.
[0070] In FIG. 1A and FIG. 1B, reference numeral 1 denotes the
optical disk medium body, 2 denotes a substantially disk-shaped
substrate (a first layer), 2a denotes a recording layer provided on
one side of the substrate 2, and 2b denotes a cover layer (a second
layer) provided on a surface of the recording layer 2a. The cover
layer 2b has a thickness smaller than that of the substrate 2, and
is formed favorably for high-density recording. The recording layer
2a sandwiched between the substrate 2 and the cover layer 2b may be
a phase change type, a magneto-optical recording type or other
types of recording layers. In the recording layer 2a, a signal
portion region is formed in which information is recorded. A laser
beam (not illustrated) enabling the recording, the reproduction and
the erasing of information is incident from a side of the cover
layer 2b. That is, a light-incident surface is a surface of the
cover layer 2b in FIG. 1B. Reference numeral 3 denotes a center
hole for centering that is provided at the center of the substrate
2. As shown in FIG. 1A, a ring-shaped convex portion 4 is provided
on a surface of the substrate 2 that is opposite to the
light-incident surface and in the vicinity of the center hole
3.
[0071] Surfaces of the substrate 2, the recording layer 2a and the
cover layer 2b that constitute the optical disk medium body 1 are
substantially flat on the respective light-incident surface sides
from the center hole 3 to the outermost periphery.
[0072] Similarly to the conventional example, reference numeral 10
denotes a hub, made of a magnetic material, having a disk form in a
substantially hat shape, and a hub hole 11 is bored at the center
of the hub to allow handling with a jig or the like. Reference
numeral 12 denotes an attracted plane in a planar disk form that
occupies most of the hub 10, 14 denotes a wall extending in a
direction substantially perpendicular to the attracted plane 12,
and 13 denotes a flange that is substantially perpendicular to the
wall 14 and extends outwardly substantially in parallel with the
attracted plane 12. The outer diameter of the flange 13 is smaller
than the inner diameter of the convex portion 4.
[0073] From the state shown in FIG. 1A, the flange 13 of the hub 10
is inserted inside the convex portion 4 so as to bring a lower
surface of the flange 13 into contact with an upper surface of the
substrate 2. In this step, since the outer diameter of the flange
13 is smaller than the inner diameter of the convex portion 4, the
hub 10 is movable horizontally with respect to the substrate 2
within a range of a difference between the inner diameter and the
outer diameter.
[0074] Thereafter, heat and pressure, for example, are applied to
an inner portion of the ring-shaped convex portion 4 so as to
thermally deform the same, whereby, as shown in FIG. 1B, a
protrusion 7 is formed so as to protrude in a horizontal direction
and cover an upper surface of the flange 13. As a result, the
flange 13 is confined with the substrate 2 by means of a
confinement portion 8 that is formed in a substantially "" shape in
cross section. Herein, the protrusion 7 is formed so that its lower
surface does not contact with the flange 13. Thereby, the hub 10 is
confined with the substrate 2 while keeping a state where the
movability of the hub is ensured with respect to the substrate 2 in
the horizontal direction and in the height direction.
[0075] Referring to FIG. 1C and FIG. 1D, a procedure for mounting
the thus configured optical disk medium 20 on a turntable will be
explained below, where the turntable is attached to a rotary shaft
of a spindle motor of the driving device (not illustrated). In FIG.
1C, reference numeral 120 denotes the turntable, at the center of
which a convex portion 123 having a cylindrical surface protrudes
so as to include a permanent magnet 121 embedded therein. The
convex portion 123 of the turntable 120 is inserted into the center
hole 3 from the side of the cover layer 2b of the optical disk
medium body 1. In this step, a tapered portion 124 at the top of
the convex portion 123 enables the correction (centering) of the
displacement of the center of the optical disk medium body 1 from
the rotation center of the turntable 120. Then, as shown in FIG.
1D, a magnetic attractive force by the permanent magnet 121 acts on
the attracted plane 12 of the hub 10 so that the edge of the
optical disk medium body 1 along the center hole 3 is positioned
between the flange 13 of the hub 10 and the turntable 120, whereby
the optical disk medium body 1 is held onto the turntable 120. In
this step, a lower surface of the cover layer 2b makes contact with
an upper surface of a flange 122 that is formed at the edge of the
turntable 120. Thereby, the optical disk medium body 1 is
positioned in a direction of the rotary shaft (the height
direction). Furthermore, an inner wall surface of the center hole 3
of the optical disk medium body 1 makes contact with an outer wall
surface of the convex portion 123 protruding from the center of the
turntable 120, whereby the optical disk medium body 1 is positioned
in the radius direction.
[0076] In the present embodiment, unlike the conventional example
shown in FIG. 12C, the optical disk medium is mounted on the
turntable 120 from the side opposite to the substrate 2.
[0077] In this state, a collected light beam is applied from the
side of the cover layer 2b. The laser beam passes through the cover
layer 2b and is converged on the recording layer 2a. The
reproduction of information is enabled by detecting reflected light
that has been modulated in accordance with the information recorded
on the recording layer 2a and demodulating the same.
[0078] In the case of a phase-change type recording layer 2a and
the like, the recording and the erasing of information are enabled
by applying heat to the recording layer 2a by irradiation with an
intense laser beam. In the case of a magneto-optical recording type
recording layer 2a, the recording and the erasing are enabled by
the concurrent use of an external magnetic field.
[0079] When the optical disk medium 20 undergoes a change in
temperature and humidity, the substrate 2 and the hub 10 have
different forms and amounts of deformation due to the change in
temperature and moisture absorption. However, since the hub 10 is
confined while keeping a movable state with respect to the
substrate 2 as described above, the warp of the optical disk medium
body 1 and the occurrence of internal stress can be avoided by
setting a difference between the inner diameter of the convex
portion 4 and the outer diameter of the flange 13 at a value with
consideration given to the differences in the forms and the amounts
of the deformation.
[0080] In the present embodiment, the surface of the cover layer 2b
that is provided on the light-incident surface side of the optical
disk medium body 1 is flat, and does not have a protrusion like the
convex portion 104 that is provided on the substrate 102 that
doubles as the cover layer as in the conventional example shown in
FIG. 12B. Therefore, the cover layer 2b can be formed thin and
uniform in thickness easily. Hence, the cover layer 2b with a
reduced optical aberration and excellent optical properties can be
formed easily. Therefore, the resolution can be enhanced, thus
enabling high density recording.
[0081] In the conventional example shown in FIG. 12B, the lower
surface 104a of the convex portion 104 makes contact with the upper
surface of the flange 122 of the turntable 120. In general, it is
difficult to control strictly the height of the convex portion 104
that protrudes like a ring shape from a plane. Therefore, when the
optical disk medium 100 is mounted on the turntable 120, a
variation in height of the convex portion 104 causes a variation in
distance between the upper surface of the flange 122 and the
recording layer 102a, which causes a variation in distance between
the objective lens of the optical head and the recording layer
102a. This results in a problem of a failure in the convergence of
a laser beam on the recording layer 102a, thus degrading the
accuracy of recording/reproduction of information. On the other
hand, according to the present embodiment, the cover layer 2b
itself makes contact with the upper surface of the flange 122 of
the turntable 120, where the entire surface of the cover layer 2b
is flat. Since the control of the thickness of the cover layer 2b
is easier than the control of the height of the convex portion 104,
the variation in distance between the upper surface of the flange
122 and the recording layer 2a can be decreased, which results in
the enhancement of the accuracy of recording/reproduction of
information.
[0082] Note here that, as a method of fixing the hub 10 to the
substrate 2, in FIG. 1B, the inner portion only of the ring-shaped
convex portion 4 is deformed so as to form the protrusion 7 to
confine the hub 10. However, the present invention is not limited
to this and the convex portion 4 may be deformed as a whole, for
example.
[0083] (Embodiment 2)
[0084] FIG. 2A is an exploded cross-sectional view of an optical
disk medium body and a hub that constitute an optical disk medium
of Embodiment 2 of the present invention, and FIG. 2B is a
cross-sectional view of the optical disk medium of Embodiment 2 of
the present invention. The following is a description of Embodiment
2 that mainly concerns the differences from Embodiment 1.
[0085] In FIG. 2A and FIG. 2B, reference numeral 21 denotes an
optical disk medium body, 22 denotes a substantially disk-shaped
substrate (a first layer), 22a denotes a recording layer provided
on one side of the substrate 22, and 22b denotes a cover layer (a
second layer) provided on a surface of the recording layer 22a. The
cover layer 22b has a thickness smaller than that of the substrate
22 and is formed favorably for high-density recording. The
recording layer 22a sandwiched between the substrate 22 and the
cover layer 22b may be a phase change type, a magneto-optical
recording type or other types of recording layers. In the recording
layer 22a, a signal portion region is formed in which information
is recorded. A laser beam (not illustrated) enabling the recording,
the reproduction and the erasing of information is incident from a
side of the cover layer 22b. That is, a light-incident surface is a
surface of the cover layer 22b in FIG. 2B. Reference numeral 23
denotes a center hole for centering that is provided at the center
of the substrate 22.
[0086] In the present embodiment, a thickness of the substrate 22
except an edge along the center hole 23 is thicker than the
thickness of the substrate 2 of Embodiment 1. In addition, a
ring-shaped concave portion 26 is provided on the surface of the
substrate 22 that is opposite to the light-incident surface side
and at the edge along the center hole 23. In the present
embodiment, the convex portion 4 shown in FIG. 1A is not
provided.
[0087] Surfaces of the substrate 22, the recording layer 22a and
the cover layer 22b that constitute the optical disk medium body 21
are substantially flat on the respective light-incident surface
sides from the center hole 23 to the outermost periphery.
[0088] Reference numeral 10 denotes a hub, which is the same as the
hub 10 described in Embodiment 1. The hub 10 has an attracted plane
12, a flange 13 and a wall 14, and a hub hole 11 is bored at the
center of the attracted plane 12. The outer diameter of the flange
13 is smaller than the inner diameter of the concave portion
26.
[0089] From the state shown in FIG. 2A, the flange 13 of the hub 10
is inserted inside the concave portion 26 so as to bring a lower
surface of the flange 13 into contact with a bottom surface 26a of
the concave portion 26. In this step, since the outer diameter of
the flange 13 is smaller than the inner diameter of the concave
portion 26, the hub 10 is movable horizontally with respect to the
substrate 22 within a range of the difference between the inner
diameter and the outer diameter.
[0090] Thereafter, heat and pressure, for example, are applied to
the edge of the ring-shaped concave portion 26 so as to thermally
deform the same, whereby, as shown in FIG. 2B, a protrusion 27 is
formed so as to protrude in a horizontal direction and cover an
upper surface of the flange 13. As a result, the flange 13 is
confined with the substrate 22 by means of a confinement portion 28
that is formed in a substantially "" shape in cross section.
Herein, the protrusion 27 is formed so that its lower surface does
not contact with the flange 13. Thereby, the hub 10 is confined
with the substrate 22 while keeping the movability of the hub 10
with respect to the substrate 22 in the horizontal direction and in
the height direction.
[0091] A procedure for mounting the thus configured optical disk
medium 30 on a turntable that is attached to a rotary shaft of a
spindle motor of the driving device is similar to that of
Embodiment 1. That is, the turntable is inserted into the center
hole 3 from the side of the cover layer 22b of the optical disk
medium 30. In the course of the accessing of the turntable to the
optical disk medium 30, a convex portion 123 of the turntable (See
FIG. 1C) is engaged with the center hole 23, whereby the positional
displacement of the center of the optical disk medium body 21 from
the rotation center of the turntable can be corrected. When the
cover layer 22b makes contact with an upper surface of a flange 122
(See FIG. 1C) that is formed at the edge of the turntable, the
mounting operation is completed.
[0092] The operations of recording, reproduction and erasing with
respect to the optical disk medium 30 of the present embodiment and
the advantages over the conventional example are the same as those
described in Embodiment 1, whose descriptions omitted.
[0093] Since the substrate 22 of the present embodiment is thicker
than that of the substrate 2 of Embodiment 1, the concave portion
26 can be formed on the surface opposite to the light-incident
surface instead of the convex portion 4. As a result, the
confinement portion 28 can be provided within a range of the
thickness of the substrate 22 in Embodiment 2, whereas the
confinement portion 8 of Embodiment 1 is provided outside a range
of the thickness of the substrate 2. Herein, the confinement
portion being within a range of the thickness of the substrate
refers to the state where a range occupied by the confinement
portion in the height direction is included in a range occupied by
the major regions of the substrate except the convex portion 4 and
the concave portion 26 at the edge along the center hole, and the
confinement portion being outside a range of the thickness of the
substrate refers to the state where a range occupied by the
confinement portion in the height direction does not overlap with a
range occupied by the major regions of the substrate except the
convex portion 4 and the concave portion 26 at the edge along the
center hole. As compared with Embodiment 1 in which the convex
portion 4 is formed on the surface of the substrate 2, the present
embodiment whose concave portion 26 is formed in the substrate 22
facilitates the formation of the substrate 22 and can enhance the
flatness of the substrate 22. Furthermore, the unevenness of the
surfaces of the optical disk medium 30 can be reduced.
[0094] (Embodiment 3)
[0095] FIG. 3A is a plan view of an optical disk medium body of
Embodiment 3 of the present invention, and FIG. 3B is a
cross-sectional view taken along an arrow 3B-3B of FIG. 3A.
[0096] In FIG. 3A and FIG. 3B, reference numeral 41 denotes an
optical disk medium body, 42 denotes a substantially disk-shaped
substrate (a first layer), 42a denotes a recording layer provided
on one side of the substrate 42, and 42b denotes a cover layer (a
second layer) provided on a surface of the recording layer 42a. The
cover layer 42b has a thickness smaller than that of the substrate
42, and is formed favorably for high-density recording. The
recording layer 42a sandwiched between the substrate 42 and the
cover layer 42b may be a phase change type, a magneto-optical
recording type or other types of recording layers. In the recording
layer 42a, a signal portion region is formed in which information
is recorded. A laser beam (not illustrated) enabling the recording,
the reproduction and the erasing of information is incident from a
side of the cover layer 42b. That is, a light-incident surface is a
surface of the cover layer 42b in FIG. 3B. Reference numeral 43
denotes a center hole for centering that is provided at the center
of the substrate 42.
[0097] At two opposed parts of the edge along the center hole 43,
cut-away portions 48 are provided. At edges of the respective
cut-away portions 48, concave portions 46 are provided on a surface
on the light-incident surface side. The depth of the concave
portions 46 measured from a turntable fitting surface is defined as
H. The thickness of the optical disk medium body 41 at the portion
where the concave portion 46 is formed is defined as T. In the case
of the present embodiment, the surface of the cover layer 42b
corresponds to the turntable fitting surface.
[0098] Surfaces of the substrate 42, the recording layer 42a and
the cover layer 42b that constitute the optical disk medium body 41
are substantially flat on the respective light-incident surface
sides from the center hole 43 to the outermost periphery (except
for the concave portions 46).
[0099] FIG. 4A is a plan view of a hub of Embodiment 3 of the
present invention, FIG. 4B is a cross-sectional view taken along an
arrow 4B-4B of FIG. 4A and FIG. 4C is a cross-sectional view taken
along an arrow 4C-4C of FIG. 4A.
[0100] In FIG. 4A to FIG. 4C, reference numeral 50 denotes a hub,
made of a magnetic material, having a disk form like a
substantially hat shape, and a hub hole 51 is bored at the center
of the hub to allow handling with a jig or the like. Reference
numeral 52 denotes an attracted plane in a planar disk form that
occupies most of the hub 50. Reference numeral 57 denotes four
slits that are formed from the edge of the hub 50 to reach the
attracted plane 52. The edge of the hub 50 is divided into two
pairs of mutually opposed regions by the four slits 57.
[0101] In one of the two pairs of regions, a pair of flanges 53 is
formed as a plurality of first latching strips. As shown in FIG.
4C, walls 58 are provided to extend in a direction substantially
perpendicular to the attracted plane 52, and the flanges 53 are
provided to extend in a direction substantially perpendicular to
the walls 58. As a result, the pair of flanges 53 extends outwardly
substantially in parallel with the attracted plane 52 and at a
position different from the attracted plane 52 in the height
direction.
[0102] In the other pair of regions, a pair of hook portions 56 is
formed as a plurality of second latching strips. As shown in FIG.
4B, two leg portions 55 are provided to extend in a direction
substantially perpendicular to the attracted plane 52, and the hook
portions 56 are provided at the respective tip ends of the leg
portions 55 so as to extend in a direction substantially
perpendicular to the leg portions 55. As a result, the pair of hook
portions 56 extends outwardly substantially in parallel with the
attracted plane 52 and at a position different from the attracted
plane 52 in the height direction. The thickness of the hook
portions 56 is defined as h. The distance between the flange 53 and
the hook portion 56 in a direction of the normal of the attracted
plane 52 is defined as L.
[0103] The thickness h of the hook portions 56 is smaller than the
depth H of the concave portions 46. In other words, they satisfy
the relationship of H>h.
[0104] Furthermore, the surface of each of the hook portions 56 on
the distant side from the attracted plane 52 (the lower surface of
the hook portion 56 in FIG. 4B) is provided with a slanting surface
56a that slants to be closer to the attracted plane 52 side (the
upper side in FIG. 4B) with increasing proximity to the tip
end.
[0105] As shown in FIG. 4B, the attracted plane 52, the flange 53
and the hook portion 56 are disposed in this order from the top in
the height direction. Thus, the length of the leg portion 55 is
longer than the length of the wall 58 in the height direction.
Moreover, the distance along the edge of the hub 50 between the
pair of slits 57 that sandwich the leg portion 55 is smaller than
the distance along the edge of the hub 50 between the pair of slits
57 that sandwich the flange 53. As a result, the leg portions 55
can be bent and deformed elastically with respect to the attracted
plane 52, and the hook portions 56 can be displaced elastically in
a direction substantially parallel with the attracted plane 52. On
the contrary, the walls 58 hardly can be deformed, and the flanges
53 are formed rigidly with the attracted plane 52.
[0106] In this way, the hub 50 is provided with the flanges 53 as
the first latching strips having high stiffness and with the hook
portions 56 as the second latching strips that can be displaced
elastically, and the flanges 53 and the hook portions 56 are
separated from each other in the height direction (the direction of
the normal of the attracted plane 52) so as to form a
double-layered latching strip group.
[0107] The diameter D.sub.h0 of the circumscribed circle for the
pair of leg portions 55 is smaller than the diameter D.sub.d1 of
the inscribed circle for the edges of the pair of cut-away portions
48 of the substrate 42. The diameter D.sub.h2 of the circumscribed
circle for the tip ends of the pair of hook portions 56 is smaller
than the diameter D.sub.d2 of the inscribed circle for the pair of
concave portions 46 and is larger than the diameter D.sub.d1 of the
inscribed circle for the edges of the pair of cut-away portions 48.
Furthermore, the diameter D.sub.h1 of the inscribed circle for the
pair of leg portions 55 is larger than the diameter D.sub.d0 of the
inscribed circle for the center hole 43. Furthermore, the diameter
D.sub.h4 of the circumscribed circle for the tip ends of the pair
of flanges 53 also is larger than the diameter D.sub.d0 of the
inscribed circle for the center hole 43. Moreover, the distance L
between the flange 53 and the hook portion 56 is larger than the
thickness T of the optical disk medium body 41 at the portion in
which the concave portion 46 is formed.
[0108] In the case where the driving device is equipped with a
mechanical mounting mechanism, the optical disk medium body 41 can
be mounted on the turntable without the use of the hub 50.
[0109] That is to say, the center hole 43 enables the centering
with respect to the turntable and the mechanism inside the driving
device allows the optical disk medium body 41 to be mounted on the
turntable. As the mounting mechanism, a known mounting means for
CDs is available, for example. The cut-away portions 48 and the
concave portions 46 do not form any obstacles to this mounting
operation.
[0110] On the other hand, when the hub 50 is attached to the
optical disk medium body 41 so as to cover the center hole 43, the
optical disk medium body 41 can be mounted on the turntable that
utilizes a magnetic attractive force.
[0111] As shown in FIG. 5A, when the hub 50 is inserted to the
optical disk medium body 41 from above, the slanting surfaces 56a
at the lower surfaces of the pair of hook portions 56 make contact
with the edges of the pair of cut-away portions 48 and the pair of
leg portions 55 is elastically deformed inwardly, respectively, so
that the pair of hook portions 56 passes between the pair of
cut-away portions 48. Thereafter, the pair of leg portions 55 is
restored elastically so that the pair of hook portions 56 is fitted
into the pair of concave portions 46. At this time, the flanges 53
make contact with the upper surface of the substrate 42. As a
result, the hub 50 is attached to the optical disk medium body 41
as shown in FIG. 5B, thus obtaining the optical disk medium 40.
[0112] The diameter D.sub.h2 of the circumscribed circle for the
tip ends of the pair of hook portions 56 is larger than the
diameter D.sub.d1 of the inscribed circle for the edges of the pair
of cut-away portions 48, and the diameter D.sub.h4 of the
circumscribed circle for the tip ends of the pair of flanges 53 is
larger than the diameter D.sub.d0 of the inscribed circle for the
center hole 43, and therefore the pair of hook portions 56 and the
pair of flanges 53 catch the substrate 42. Thus, the hub 50 does
not fall from the substrate 42.
[0113] Furthermore, the distance L between the flange 53 and the
hook portion 56 is larger than the thickness T of the optical disk
medium body 41 at the portion in which the concave portion 46 is
formed. In addition, the diameter D.sub.h0 of the circumscribed
circle for the pair of leg portions 55 is smaller than the diameter
D.sub.d1 of the inscribed circle for the edges of the pair of
cut-away portions 48. Moreover, the diameter D.sub.h2 of the
circumscribed circle for the tip ends of the pair of hook portions
56 is smaller than the diameter D.sub.d2 of the inscribed circle
for the pair of concave portions 46. From these, the hub 50 is
movable within a limited range in the horizontal direction and in
the height direction with respect to the substrate 42.
[0114] Furthermore, since the depth H of the concave portions 46
and the thickness h of the hook portions 56 satisfy the
relationship of H>h, at least when the optical disk medium 40 is
mounted on the turntable, the hook portions 56 are recessed in the
concave portions 46. Therefore, the light-incident side surface of
the optical disk medium body 41 and the upper surface of the flange
122 (See FIG. 1C) of the turntable can be in contact with each
other entirely, and the hook portions 56 do not become a hindrance
to the mounting operation.
[0115] Furthermore, the diameter D.sub.h1 of the inscribed circle
for the pair of leg portions 55 is larger than the diameter
D.sub.d0 of the inscribed circle for the center hole 43, and
therefore the convex portion 123 having a cylindrical surface
protruding from the center of the turntable and the tapered portion
124 at the top of the convex portion 123 (See FIG. 1C) make contact
with the edge along the center hole 43 and not with the inner walls
of the leg portions 55. Therefore, the leg portions 55 do not
become a hindrance to the centering operation of the optical disk
medium body 41.
[0116] The present embodiment further has the following specific
effects in addition to the advantages of Embodiments 1 and 2. That
is, the optical disk medium body 41 can be sold without the hub 50
being attached thereto. In this case, the cost of the hub 50 and
the assembly cost of the optical disk medium body 41 can be
reduced. Therefore, the optical disk medium body 41 can be provided
at a low cost, which facilitates, for example, the distribution of
the optical disk medium body 41 that is attached to a publication
and the like. In this case, the configuration without a protrusion
formed by the hub 50 also acts as a big advantage.
[0117] In the case where a driving device equipped with a
mechanical mounting mechanism is used, the optical disk medium body
41 alone can be mounted without the use of the hub 50 as stated
above and can be used. Alternatively, a user who uses a driving
device equipped with a mounting mechanism utilizing a magnetic
attractive force may get a hub 50 if needed and attach the hub 50
to the optical disk medium body 41 by himself/herself so as to use
the same.
[0118] Needless to say, a manufacturer can sell the optical disk
medium 40 shown in FIG. 5B in which the hub 50 has been attached to
the optical disk medium body 41. In this case, the hub 50 can be
attached to the optical disk medium body 41 without the necessity
of specific capital investment, and therefore the manufacturing
cost can be reduced.
[0119] The optical disk medium body 41 of the present embodiment is
provided with the concave portion 46 on the light-incident surface
side. Unlike the convex portion 104 shown in FIG. 12B, this concave
portion 46 hardly becomes a hindrance to the formation of a thin
cover layer 42b with a uniform thickness. In this way,
substantially no protrusions are formed on the surface of the
optical disk medium body 41 of the present embodiment on the
light-incident surface side, which facilitates the formation of the
cover layer 42b with excellent optical properties.
[0120] (Embodiment 4)
[0121] FIG. 6A is a plan view of a hub of Embodiment 4 of the
present invention, and FIG. 6B is a cross-sectional view taken
along an arrow 6B-6B of FIG. 6A.
[0122] In FIG. 6A and FIG. 6B, reference numeral 70 denotes a hub,
made of a magnetic material, having a substantially disk form, and
a hub hole 71 is bored at the center of the hub to allow handling
with a jig or the like. Reference numeral 72 denotes an attracted
plane in a planar disk form that occupies most of the hub 70.
Reference numeral 77 denotes four slits that are formed from the
edge of the hub 70. The edge of the hub 70 is divided into two
pairs of mutually opposed regions by the four slits 77.
[0123] In one of the two pairs of regions, a pair of flanges 73 is
formed substantially coplanar with the attracted plane 72 as a
plurality of first latching strips. The following describes the
case where the flanges 73 are provided coplanar with the attracted
plane 72.
[0124] In the other pair of regions, a pair of hook portions 76 is
formed as a plurality of second latching strips. As shown in FIG.
6B, two leg portions 75 are provided to extend in a direction
substantially perpendicular to the attracted plane 72, and the hook
portions 76 are provided at the respective tip ends of the leg
portions 75 so as to extend in a direction substantially
perpendicular to the leg portions 75. As a result, the pair of hook
portions 76 extends outwardly substantially in parallel with the
attracted plane 72 and at a position different from the attracted
plane 72 and the flanges 73 in the height direction. The thickness
of the hook portions 76 is defined as h. The distance between the
flange 73 and the hook portion 76 in a direction of the normal of
the attracted plane 72 is defined as L.
[0125] Furthermore, the surface of each of the hook portions 76 on
the distant side from the attracted plane 72 (the lower surface of
the hook portions 76 in FIG. 6B) is provided with a slanting
surface 76a that slants to be closer to the attracted plane 72 side
(the upper side in FIG. 6B) with increasing proximity to the tip
end.
[0126] As shown in FIG. 6B, the attracted plane 72 and the flanges
73 are located at the same height in the height direction, and the
hook portion 76 is disposed below these. The distance along the
edge of the hub 70 between the pair of slits 77 that sandwich the
leg portion 75 is smaller than the distance along the edge of the
hub 70 between the pair of slits 77 that sandwich the flange 73. As
a result, the leg portions 75 can be bent and deformed elastically
with respect to the attracted plane 72, and the hook portions 76
can be displaced elastically in a direction substantially parallel
with the attracted plane 72. On the contrary, the flanges 73 are
formed rigidly with the attracted plane 72.
[0127] In this way, the hub 70 is provided with the flanges 73 as
the first latching strips having high stiffness and with the hook
portions 76 as the second latching strips that can be displaced
elastically, and the flanges 73 and the hook portions 76 are
separated from each other in the height direction (the direction of
the normal of the attracted plane 72) so as to form a
double-layered latching strip group.
[0128] FIG. 7A is an exploded cross-sectional view of an optical
disk medium body and the hub that constitute the optical disk
medium of Embodiment 4 of the present invention, and FIG. 7B is a
cross-sectional view of the optical disk medium of Embodiment 4 of
the present invention.
[0129] In FIG. 7A and FIG. 7B, reference numeral 61 denotes an
optical disk medium body and 62 denotes a substantially disk-shaped
substrate (a first layer). The optical disk medium body 61 of the
present embodiment is the same as the optical disk medium body 41
of Embodiment 3 as a whole except that the substrate 62 is thicker
than the substrate 42. A recording layer 62a, a cover layer 62b and
a center hole 63 are the same as the recording layer 42a, the cover
layer 42b and the center hole 43 of Embodiment 3, respectively.
[0130] Similarly to Embodiment 3, at two opposed parts of the edge
along the center hole 63, cut-away portions 68 are provided. At
edges of the respective cut-away portions 68, concave portions 66
are provided on a surface on the light-incident surface side. The
depth of the concave portion 66 measured from a turntable fitting
surface is defined as H. The thickness of the optical disk medium
body 61 at the portion where the concave portion 66 is formed is
defined as T. In the case of the present embodiment, the surface of
the cover layer 62b corresponds to the turntable fitting
surface.
[0131] Similarly to Embodiment 3, the thickness h of the hook
portions 76 of the hub 70 is smaller than the depth H of the
concave portions 66. In other words, they satisfy the relationship
of H>h.
[0132] Surfaces of the substrate 62, the recording layer 62a and
the cover layer 62b that constitute the optical disk medium body 61
are substantially flat on the respective light-incident surface
sides from the center hole 63 to the outermost periphery (except
for the concave portions 66).
[0133] The diameter D.sub.h0 of the circumscribed circle for the
pair of leg portions 75 is smaller than the diameter D.sub.d1 of
the inscribed circle for the edges of the pair of cut-away portions
68 of the substrate 62. The diameter D.sub.h2 of the circumscribed
circle for the tip ends of the pair of hook portions 76 is smaller
than the diameter D.sub.d2 of the inscribed circle for the pair of
concave portions 66 and is larger than the diameter D.sub.d1 of the
inscribed circle for the edges of the pair of cut-away portions 68.
Furthermore, the diameter D.sub.h1 of the inscribed circle for the
pair of leg portions 75 is larger than the diameter D.sub.d0 of the
inscribed circle for the center hole 63. Furthermore, the diameter
D.sub.h4 of the circumscribed circle for the tip ends of the pair
of flanges 73 also is larger than the diameter D.sub.d0 of the
inscribed circle for the center hole 63. Moreover, the distance L
between the flange 73 and the hook portion 76 is larger than the
thickness T of the optical disk medium body 61 at the portion in
which the concave portion 66 is formed.
[0134] In the case where the driving device is equipped with a
mechanical mounting mechanism, the optical disk medium body 61 can
be mounted on the turntable without the use of the hub 70.
[0135] That is to say, the center hole 63 enables the centering
with respect to the turntable and the mechanism inside the driving
device allows the optical disk medium body 61 to be mounted on the
turntable. As the mounting mechanism, a known mounting means for
CDs is available, for example. The cut-away portions 68 and the
concave portions 66 do not form any obstacles to this mounting
operation.
[0136] On the other hand, when the hub 70 is attached to the
optical disk medium body 61 so as to cover the center hole 63, the
optical disk medium body 61 can be mounted on the turntable that
utilizes a magnetic attractive force.
[0137] Similarly to Embodiment 3, as shown in FIG. 7A, when the hub
70 is inserted to the optical disk medium body 61 from above, the
slanting surfaces 76a at the lower surfaces of the pair of hook
portions 76 make contact with the edges of the pair of cut-away
portions 68 and the pair of leg portions 75 is elastically deformed
inwardly, respectively, so that the pair of hook portions 76 passes
between the pair of cut-away portions 68. Thereafter, the pair of
leg portions 75 is restored elastically so that the pair of hook
portions 76 is fitted into the concave portions 66. At this time,
the flanges 73 make contact with the upper surface of the substrate
62. As a result, the hub 70 is attached to the optical disk medium
body 61 as shown in FIG. 7B, thus obtaining the optical disk medium
60.
[0138] The diameter D.sub.h2 of the circumscribed circle for the
tip ends of the pair of hook portions 76 is larger than the
diameter D.sub.d1 of the inscribed circle for the edges of the pair
of cut-away portions 68, and the diameter D.sub.h4 of the
circumscribed circle for the tip ends of the pair of flanges 73 is
larger than the diameter D.sub.d0 of the inscribed circle for the
center hole 63, and therefore the pair of hook portions 76 and the
pair of flanges 73 catch the substrate 62. Thus, the hub 70 does
not fall from the substrate 62.
[0139] Furthermore, the distance L between the flange 73 and the
hook portion 76 is larger than the thickness T of the optical disk
medium body 61 at the portion in which the concave portion 66 is
formed. In addition, the diameter D.sub.h0 of the circumscribed
circle for the pair of leg portions 75 is smaller than the diameter
D.sub.d1 of the inscribed circle for the edges of the pair of
cut-away portions 68. Moreover, the diameter D.sub.h2 of the
circumscribed circle for the tip ends of the pair of hook portions
76 is smaller than the diameter D.sub.d2 of the inscribed circle
for the pair of concave portions 66. From these, the hub 70 is
movable within a limited range in the horizontal direction and in
the height direction with respect to the substrate 62.
[0140] Furthermore, since the depth H of the concave portions 66
and the thickness h of the hook portions 76 satisfy the
relationship of H>h, at least when the optical disk medium 60 is
mounted on the turntable, the hook portions 76 are recessed in the
concave portions 66. Therefore, the light-incident side surface of
the optical disk medium body 61 and the upper surface of the flange
122 (See FIG. 1C) of the turntable can be in contact with each
other entirely, and the hook portions 76 do not become a hindrance
to the mounting operation.
[0141] Furthermore, the diameter D.sub.h1 of the inscribed circle
for the pair of leg portions 75 is larger than the diameter
D.sub.d0 of the inscribed circle for the center hole 63, and
therefore the convex portion 123 having a cylindrical surface
protruding from the center of the turntable and the tapered portion
124 at the top of the convex portion 123 (See FIG. 1C) make contact
with the edge along the center hole 63 and not with the inner walls
of the leg portions 75. Therefore, the leg portions 75 do not
become a hindrance to the centering operation of the optical disk
medium body 61.
[0142] In addition to the advantages of the availability of the
optical disk medium body 61 alone and the capability of the
attachment of the hub 70 as needed, which are similar to advantages
of Embodiment 3, the present embodiment has another advantage of
the enhancement of the accuracy of form because the flanges 73 of
the hub 70 are formed substantially coplanar with the attracted
plane 72.
[0143] (Embodiment 5)
[0144] FIG. 8 is a plan view of an optical disk medium body 81 of
Embodiment 5 of the present invention. The optical disk medium body
81 of the present embodiment is different from the optical disk
medium body 41 of Embodiment 3 in that cut-away portions 88 and
concave portions 86 are provided at three points spaced at
substantially equal angles at the edge along a center hole 83,
whereas the cut-away portions 48 and the concave portions 46 of the
optical disk medium body 41 of Embodiment 3 are provided at two
mutually opposed points of the edge along the center hole 43. The
cut-away portions 88 and the concave portions 86 are substantially
the same as the cut-away portions 48 and the concave portions 46,
respectively. The remaining configuration of the optical disk
medium body 81 of the present embodiment is approximately the same
as that of the optical disk medium body 41 of Embodiment 3.
[0145] FIG. 9 is a plan view of a hub 90 of Embodiment 5 of the
present invention. The hub 90 of the present embodiment is
different from the hub 50 of Embodiment 3 in that leg portions 95
and hook portions 96 are provided at three points spaced at
substantially equal angles at the edge of an attracted plane 92 so
as to be adapted to the optical disk medium body 81, whereas the
leg portions 55 and the hook portions 56 are provided at two
mutually opposed points at the edge of the attracted plane 52 of
the hub 50 of Embodiment 3. The leg potions 95 and the hook
portions 96 are substantially the same as the leg portions 55 and
the hook portions 56, respectively. The remaining configuration of
the hub 90 of the present embodiment is approximately the same as
that of the hub 50 of Embodiment 3.
[0146] The details of the present embodiment have been omitted,
because they are substantially the same as those described in
Embodiment 3. The specific effect of the present embodiment in
contrast with Embodiment 3 resides in that the hub 90 is connected
with the optical disk medium body 81 more stably because the
optical disk medium body 81 and the hub 90 are engaged at three
points. This leads to the effect of significantly reducing the
possibility of the hub 90 falling out when subjected to an impact
due to dropping, for example.
[0147] In the present invention, the connecting configuration of
the optical disk medium body with the hub and the number of
engagement portions made up of the cut-away portions and the
concave portions provided in the optical disk medium body and the
leg portions and the hook portions provided in the hub are not
limited to those described in the above Embodiments 3 to 5, and
they can be changed variously within a scope of the present
invention.
[0148] (Embodiment 6)
[0149] The following describes a preferable numerical range
concerning a portion where the hub is attached to the optical disk
medium body.
[0150] FIG. 10 is an expanded cross-sectional view of a portion in
the vicinity of a center hole of an optical disk medium of
Embodiment 6 of the present invention. The optical disk medium of
FIG. 10 has the same configuration as that of the optical disk
medium 20 (See FIG. 1B) described in Embodiment 1, and therefore
the same reference numerals are assigned to the same elements as
those in Embodiment 1 and their detailed explanations omitted.
[0151] Experiments were conducted in order to determine the
preferable numerical range of various dimensions of the portions in
the vicinity of the center hole 3. The details of the experiments
are as follows:
[0152] The substrate 2 was made of polycarbonate, whose outer
diameter was 54 mm and thickness was 0.6 mm. A material of the hub
10 was stainless steel having magnetic properties.
[0153] The attachment of the hub 10 to the optical disk medium body
1 was as described in Embodiment 1. That is to say, as shown in
FIG. 1A, the hub 10 was inserted inside the ring-shaped convex
portion 4 surrounding the center hole 3, and the internal portion
of the upper surface of the convex portion 4 was melted by an
ultrasonic welding method and was deformed by a pressure applied
thereto, whereby the protrusion 7 covering the flange 13 of the hub
10 was formed. In this step, the melting amount was controlled so
as to ensure a gap between the confinement portion 8 whose
cross-section would be shaped a substantially "" shape and the
flange 13, which allowed the hub 10 to move freely with respect to
the optical disk medium body 1 within a limited range.
[0154] In the case where the hub 10 and the substrate 2 are adhered
completely, there is a probability that the optical disk medium
body 1 is mounted on the turntable 120 in an off-center state when
the optical disk medium 20 is mounted on the turntable 120 of the
driving device. If the hub 10 is movable with respect to the
optical disk medium body 1, the tapered portion 124 of the
turntable 120 easily exerts the centering function for the center
hole 3.
[0155] Firstly, a position of a region 13a where the lower surface
of the flange 13 and the upper surface of the substrate 2 contacted
was changed from the rotation center axis, and a change in the
warped angle at the outer edge of the optical disk medium body 1
mounted on the turntable 120 was measured.
[0156] In Experiment 1, the inner diameter D.sub.d0 of the center
hole 3 was set at 11 mm. The thickness T.sub.0 of the optical disk
medium body 1 at the region 13a was set at 0.6 mm. Furthermore, as
for the ring-shaped portion of the turntable 120 that contacted
with the lower surface of the optical disk medium body 1, the inner
diameter D.sub.t1 and the outer diameter D.sub.t2 of that portion
were set at 12 mm and 13 mm, respectively. The width W of the
region 13a in the radius direction was kept constant at 1.0 mm and
the inner diameter D.sub.h5 and the outer diameter D.sub.h6 of the
region 13a were changed. Table 1 shows the results. In Table 1, the
warp is represented in a manner that positive (+) indicates the
upward warp in FIG. 10 and negative (-) indicates the downward warp
(toward the light-incident surface).
1TABLE 1 Inner Outer diameter D.sub.h5 diameter D.sub.h6 Warp (mm)
(mm) (degree) 11.0 12.0 +0.15 11.5 12.5 +0.10 11.8 12.8 +0.02 12.0
13.0 +0.02 12.3 13.3 +0.02 12.5 13.5 -0.03
[0157] From Table 1, it was found that the warp of the optical disk
medium body 1 was changed in accordance with a change in the
position of the region 13a where the lower surface of the flange 13
and the upper surface of the substrate 2 contacted.
[0158] In Experiment 2, the warp was measured in a manner similar
to the above Experiment 1 except that the inner diameter D.sub.t1
and the outer diameter D.sub.t2 of the ring-shaped portion of the
turntable 120 that contacted with the lower surface of the optical
disk medium body 1 were changed to 12.5 mm and 13.5 mm,
respectively, and the width W of the region 13a in the radius
direction was kept constant at 1.2 mm. Table 2 shows the
results.
2TABLE 2 Inner Outer diameter D.sub.h5 diameter D.sub.h6 Warp (mm)
(mm) (degree) 11.0 12.2 +0.10 11.5 12.7 +0.04 11.8 13.0 +0.01 12.0
13.2 +0.02 12.3 13.5 -0.02 12.5 13.7 -0.05
[0159] From Table 1 and Table 2, it was found that the warp of the
optical disk medium body 1 was changed also with the dimensions of
the turntable 120.
[0160] Then, in view of Table 1, as for the region 13a, the inner
diameter D.sub.h5.gtoreq.11.8 mm and the outer diameter
D.sub.h6.ltoreq.13.3 mm are preferable, and in view of Table 2, as
for the region 13a, the inner diameter D.sub.h5.gtoreq.11.8 mm and
the outer diameter D.sub.h6.ltoreq.13.5 mm are preferable.
Therefore, in the case of the inner diameter of the region 13a
D.sub.h5.gtoreq.11.8 mm and the outer diameter D.sub.h6.ltoreq.13.3
mm, the warp of the optical disk medium body 1 can be reduced for
both of the conditions in the above Experiment 1 and Experiment 2.
The inner diameter D.sub.h5.gtoreq.11.8 mm and the outer diameter
D.sub.h6.ltoreq.13.0 mm are the most preferable.
[0161] As long as the inner diameter D.sub.h5 and the outer
diameter D.sub.h6 satisfy the above-stated numerical range, there
is no need to set the width W of the region 13a in the radius
direction at 1.0 mm and 1.2 mm as in the above Experiments 1 and 2.
The width may be set larger or smaller than these values or a value
between these.
[0162] Secondly, the thickness T.sub.0 of the optical disk medium
body 1 at the region 13a was changed, and a change in the warped
angle at the outer edge of the optical disk medium body 1 mounted
on the turntable 120 was measured.
[0163] In general, the optical disk medium 20 is required to have a
smaller thickness. Herein, the thickness of the optical disk medium
20 is substantially determined by a sum of the thickness T.sub.0 of
the optical disk medium body 1 at the region 13a and the thickness
Th of the hub 10. There is a lower limit for the thickness Th of
the hub 10 in terms of the processability and the strength to be
secured. Also from the viewpoint of avoiding the collision with the
turntable 120 that is inserted into the center hole 3, there is a
lower limit for the thickness Th of the hub 10. Hence, the
thickness T.sub.0 of the region 13a is required to be smaller.
[0164] In Experiment 3, the warped angle at the outer edge of the
optical disk medium body 1 was measured, while the thickness
T.sub.0 was changed. In the conditions of the above-described
Experiment 1, the inner diameter D.sub.h5 and the outer diameter
D.sub.h6 were set at 12.0 mm and 13.0 mm, respectively. The
thickness Th of the hub 10 was set at 0.9 mm. The height Ht of the
turntable 120 at a portion inserted into the center hole 3 was set
at 1.2 mm. Table 3 shows the results.
3 TABLE 3 Thickness Warp T.sub.0 (mm) (degree) 0.3 +0.10 0.4 +0.04
0.5 +0.02 0.6 +0.02 0.7 +0.02 0.8 +0.02
[0165] From Table 3, when the thickness T.sub.0 is less than 0.5
mm, the warp of the optical disk medium body 1 increases, and the
thickness of 0.3 mm leads to a significant increase in the warp.
Therefore, the thickness T.sub.0 of the optical disk medium body 1
at the region 13a should be 0.5 mm or more.
[0166] Note here that, in this Embodiment 6, explanations have been
made taking the optical disk medium described in Embodiment 1 as an
example. However, the present embodiment can be applied similarly
to the optical disk media of Embodiments 2 to 5 as well.
Conceivably, the above-stated warp of the optical disk media
occurred because the optical disk medium body was positioned
between the hub and the turntable. Therefore, in the case of the
applications to the optical disk media of Embodiments 3 to 5, the
flange 13 of the above-stated hub 10 needs to be adapted to the
first latching strips. Thus, in the case of Embodiment 3, for
example, it is preferable that the diameter of the circle that is
inscribed in the two region where the surface of the optical disk
medium body 41 on the opposite side of the light-incident surface
and the flanges 53 of the hub 50 is 11.8 mm or more and the
diameter of the circle that is circumscribed around the two regions
is 13.3 mm or less. Furthermore, the thickness of the optical disk
medium body 41 at the portion contacting with the flanges 53
preferably is 0.5 mm or more.
[0167] In the above-described optical disk medium bodies of
Embodiments 1 to 6, the recording layers and the cover layers are
formed so as to reach the edge along the center holes. However, the
present invention is not limited to these. At a region closer to
the center hole that contacts with the turntable, with respect to
which the recording/reproduction of information is impossible
practically, the recording layer and/or the cover layer may not be
formed. Furthermore, the recording layer and/or the cover layer may
not be formed in the vicinity of the outer edge of the substrate as
well. Since the thicknesses of the recording layer and the cover
layer are so small that a level difference generated at a border
line on the substrate is small between the region where these
layers are formed and a not-forming region. In the present
invention, although a substantially flat surface of the optical
disk medium body on the light-incident surface side is preferable,
"substantially flat" in this context contemplates the presence of
such a level difference.
[0168] The embodiments disclosed in this application are intended
to illustrate the technical aspects of the invention and not to
limit the invention thereto. The invention may be embodied in other
forms without departing from the spirit and the scope of the
invention as indicated by the appended claims and is to be broadly
construed.
* * * * *